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The Autonomic Nervous System Anbar Medical College Dr. Yagub S Saleh
Dep. of Pharmacology (1) 2020-2021
Page 1 of 8
The Autonomic Nervous System The nervous system is divided into "central"
and "peripheral" nervous system.
The peripheral nervous system is divided
physiologically into afferent (sensory) and
efferent (motor-effector) nervous system.
The motor nervous system can be further
divided into "somatic" nervous system
&"autonomic" nervous system.
The autonomic nervous system consists of
three main anatomical divisions: sympathetic,
parasympathetic and enteric nervous systems.
Enteric nervous system (known as the brain
of the gut).
The Autonomic Nervous System Anbar Medical College Dr. Yagub S Saleh
Dep. of Pharmacology (1) 2020-2021
Page 2 of 8
Neurotransmitters
Acetylcholine (ACh) and norepinephrine (NE) are the two major neurotransmitters of the ANS
ACh is released by all preganglionic axons and all parasympathetic postganglionic axons
Cholinergic fibers – ACh-releasing fibers Adrenergic fibers – sympathetic postganglionic axons that
release NE (except for sweat glands) Neurotransmitter effects can be excitatory or inhibitory
depending upon the receptor type.
How do drugs influence the ANS? Mimic or block the effects of the two primary neurotransmitters,
Acetylcholine and Norepinephrine/Epinephrine
Drugs that mimic neurotransmitters are referred to as “receptor agonists”
o These drugs activate receptors
Drugs that block neurotransmitters are referred to as “receptor antagonists”
o These drugs block the endogenous neurotransmitters from activating
receptors
Classification of drugs affecting the ANS
Parasympathetic nervous system
Mimic acetylcholine
Cholinergic = muscarinic agonists = parasympathomimetic
Block acetylcholine
Anticholinergic = muscarinic antagonist = parasympatholytic
The Autonomic Nervous System Anbar Medical College Dr. Yagub S Saleh
Dep. of Pharmacology (1) 2020-2021
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Sympathetic nervous system
Mimic norepinephrine
Adrenergic = adrenergic agonist = sympathomimetic
Block norepinephrine
Antiadrenergic = adrenergic antagonist = sympatholytic
Cholinergic System
The Autonomic Nervous System Anbar Medical College Dr. Yagub S Saleh
Dep. of Pharmacology (1) 2020-2021
Page 4 of 8
Nicotinic Receptors
Nicotinic receptors are found on:
o Motor end plates (somatic targets)
o All ganglionic neurons of both sympathetic and parasympathetic
divisions
o The hormone-producing cells of the adrenal medulla
The effect of ACh binding to nicotinic receptors is always stimulatory
Muscarinic Receptors
Muscarinic receptors occur on all effector cells stimulated by postganglionic
cholinergic fibers
The effect of ACh binding:
o Can be either inhibitory or excitatory
o Depends on the receptor type of the target organ
Muscarinic was introduced because of the mushroom poison muscarine
The Autonomic Nervous System Anbar Medical College Dr. Yagub S Saleh
Dep. of Pharmacology (1) 2020-2021
Page 5 of 8
The Autonomic Nervous System Anbar Medical College Dr. Yagub S Saleh
Dep. of Pharmacology (1) 2020-2021
Page 6 of 8
The Autonomic Nervous System Anbar Medical College Dr. Yagub S Saleh
Dep. of Pharmacology (1) 2020-2021
Page 7 of 8
M3
Receptors and signal transduction in the ANS:
Muscarinic receptors
α1
The Autonomic Nervous System Anbar Medical College Dr. Yagub S Saleh
Dep. of Pharmacology (1) 2020-2021
Page 8 of 8
